Aneurysms occur in blood vessels at sites where, due to age, disease or genetic predisposition of the patient, the strength or resilience of the vessel wall is insufficient to prevent ballooning or stretching of the wall as blood passes through. If the aneurysm is left untreated, the blood vessel wall may expand and rupture, often resulting in death.
To prevent rupturing of an aneurysm, a stent graft may be introduced into a blood vessel percutaneously and deployed to span the aneurysmal sac. Stent grafts include a graft fabric secured to a cylindrical scaffolding or framework of one or more stents. The stent(s) provide rigidity and structure to hold the graft open in a tubular configuration as well as the outward radial force needed to create a seal between the graft and a healthy portion of the vessel wall and provide migration resistance. Blood flowing through the vessel can be channeled through the luminal surface of the stent graft to reduce, if not eliminate, the stress on the vessel wall at the location of the aneurysmal sac. Stent grafts may reduce the risk of rupture of the blood vessel wall at the aneurysmal site and allow blood to flow through the vessel without interruption.
However, various endovascular repair procedures such as the exclusion of an aneurysm require a stent graft to be implanted adjacent to a vascular bifurcation. Often the aneurysm extends into the bifurcation requiring the stent graft to be placed into the bifurcation. A bifurcated stent graft is therefore required in these cases. Modular stent grafts, having a separate main body and branch component are often preferred in these procedures due to the ease and accuracy of deployment. See U.S. Patent Application No. 2008/0114446 to Hartley et al. for an example of a modular stent graft having separate main body and branch stent components. In the Hartley et al. publication the main body stent has a fenestration in the side wall that is tailored to engage and secure the side branch stent. The side branch stent in such a configuration is in a “line to line” interference fit with the main body fenestration, causing a potential compromise to the fatigue resistance of the stent to stent junction. U.S. Pat. No. 6,645,242 to Quinn presents a more robust stent to stent joining configuration. In the Quinn patent, a tubular support, internal to the main body stent, is incorporated to enhance the reliability of the stent to stent joining. The tubular, internal support of Quinn provides an extended sealing length along with improved fatigue resistance. However, the innermost tube is made by adding additional material shaped into a tube and sewn and/or adhered to the main graft component.
In addition, Aneurysms occurring in the aorta, the largest artery in the human body, may occur in the chest (thoracic aortic aneurysm) or in the abdomen (abdominal aortic aneurysm). Due to the curvature of the aortic arch, thoracic aortic aneurysms can be particularly challenging to treat. Other parts of the vasculature, such as the common iliac artery which extends from the aorta, can also be extremely tortuous. Hence, a stent graft deployed into such regions is preferably able to conform to the vasculature. The high degree of conformability allows the stent graft to bend and optimally oppose and seal against the native vessel.